Reducing noise valve stop

Abstract: The profile of the valve stop (22) of a discharge valve (20) is configured such that the portion facing the free length of the valve member (21) has an increasing radius portion and a decreasing radius portion.

Description: The invention relates to a discharge valve assembly including a valve stop and a valve member having a tip and a root and having a clamped length at said root and a free length extending from said clamped length to said tip. A discharge valve assembly of this type is disclosed in JP-A-60-8577. In positive displacement compressors employing valves, the valve members may cycle hundreds of times per minute. Valve stops are commonly employed to protect the valve member from being overstressed by limited movement of the valve member. For example, under liquid slugging conditions, the mass flow during a cycle is such that the valve member would be excessively displaced if a valve stop was not present. Engagement of the valve stop by the valve member can be a significant source of noise. Specifically, a discharge valve stop in a rolling piston rotary compressor has been identified as one of the major noise sources through the impact kinetic energy transmission of a discharge valve member. The impact between the valve and valve stop generates significant noise radiation at the natural frequency of the valve stop due to transmission of valve kinetic energy to the valve stop and the compressor shell, where the valve stop is excited at its natural frequency. A discharge valve stop in a rotary compressor has been identified as a major noise source through the impact kinetic energy transmission of a discharge valve. A primary reason for the intensity of the noise in conventional valve stop designs is that the tip of the valve member impacts the valve stop before the root does and because total valve/valve stop contact occurs, typically during the last tenth of a millisecond of a one millisecond opening stroke. As disclosed in JP-A-60-8577 compressor discharge valve noise is reduced by the valve which is provided with a soft spring characteristic at the beginning of the opening stroke and a stronger spring characteristic at the end of the opening stroke. This is achieved in JP-A-60-8577 by a deformable retaining plate interposed between the valve and the valve stop. The retaining plate has a sharper curvature than the flexion curve of the valve from its support point to its free end, and sharper than the valve stop to create a void between the retaining plate and the valve stop. The spring characteristic of the valve is soft before it contacts the retaining plate and then stronger when the retaining plate deforms to reduce the size of the void. The object of the invention is to provide an improved reduced noise discharge valve assembly for use in compressors, such as a positive displacement hermetic compressor. The discharge valve assembly of the invention, as defined in the independent claim 1, reduces impact between the valve member and the valve stop, preferably a profile is employed such that the initial impact occurs at a time when only a small amount of kinetic energy has been developed in the valve member and continues through essentially the entire opening stroke of the valve member such that contact progresses from the root through the middle to the head of the valve member. This produces a rolling contact with a continuous contact between the valve member and stop as the valve member wraps around the stop. A smooth and gradual contact with a longer time interval transmits less spectrum rich energy and produces a smaller valve stop deflection than a short time high velocity impact. In one embodiment of the discharge valve assembly the second portion of the free length has a radius less than said first portion beyond a point generally corresponding to 90 % of said free length. The profile of the free length of the valve stop may be contoured so that engagement between said valve member and said stop takes place over essentially an entire opening movement of said valve member thereby maximizing the duration of, and minimizing the amount of, kinetic energy transfer from said valve member to said stop. The free length can be profiled so that engagement between the valve member of the valve stop avoids exciting the natural frequency of the valve stop. For a fuller understanding of the present invention, reference should be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: Figure 1 is a sectional view of a discharge valve incorporating the present invention; Figure 2 is a comparison of the profiles of the valve stop of the present invention and a conventional constant radius profile; and Figure 3 is a plot of impact momentum vs. time for the profiles of Figure 2. In Figure 1, the numeral 10 generally designates a high side, positive displacement, hermetic compressor having a shell 12. Discharge port 16 is formed in member 14 which would be the motor side bearing end cap in the case of a fixed vane or rolling piston compressor. Also in the case of a fixed vane or rolling rotor compressor, discharge port 16 will open into a muffler to attenuate pulsations prior to flowing into the interior of shell 12. Discharge port 16 is controlled by valve assembly 20 which includes valve member 21, valve stop 22 and bolt or other fastening member 23 for securing valve member 21 and valve stop 22 to member 14. In operation, when the pressure at discharge port 16 exceeds the pressure in chamber 17 adjacent to valve assembly 20, valve member 21 opens, by deforming or flexing, to permit flow through discharge port 16 into chamber 17. In the absence of valve stop 22, the valve member 21 would flex to a curved configuration during the discharge stroke and seat on discharge port 16 during the suction stroke. The valve stop 22 is only present to prevent excessive flexure of valve member 21, such as would happen during liquid slugging conditions, which would permanently deform the valve member 21. Accordingly, current designs have the valve member 21 impacting the valve stop 22 during normal operation with resultant noise. This is primarily due to the fact that the valve tip strikes the valve stop first and that impact takes place over a small percentage of the discharge stroke. The present invention configures the valve stop 22 to a shape such that impact occurs over a much larger portion of the discharge stroke with contact progressing from the root through the middle to the head of the valve member 21 as the valve member 21 wraps around the valve stop 22. Valve member 21 is very thin, typically on the order of 0.4mm, in its bending direction so the shear stress contribution to the resultant maximum principal stress can be neglected. It is assumed that the stop 22 is very thick as compared with the thickness of the valve member 21 so that the valve member 21 can be considered to be clamped at the root of the stop similar to a cantilever beam. It is also assumed that the force applied on the valve head is taken as applied at the tip of a cantilever beam which corresponds to the head center of the valve member 21. Turning now to Figure 2, curve A designates a standard fixed radius stop profile having a fixed center point E, specifically a 38mm radius, and curve B designates the profile of the present invention. As illustrated, the stop profiles represent a valve member having a free length of approximately 27mm and a clamped length of approximately 10mm. For the free length portion of curve B, relative to curve A, there is an increasing radius portion and a decreasing radius portion with the transition coming at a free length of approximately 17mm. In the increasing radius portion the radius or distance of curve B to the center E increases in a direction away from the clamped length and in the decreasing, radius portion the radius or distance of curve B to the center E decreases in a direction away from the clamped length. Comparing curves A and B it will be noted that the curves do not intersect until a free length of approximately 24mm. It follows, that as compared to a standard constant radius stop profile the present invention has a lesser height for approximately 90% of the free length and a greater height for approximately the last 10% of the free length. The sharper curvature of curve B occurring at a greater free length has the effect of increasing the time it takes for the valve member 21 to complete the contact process with stop 22, and results in less of the valve member 21 making impact, thereby reducing the transferred momentum. The combination of increased contact time and reduced transferred momentum greatly suppresses the valve-valve stop vibration and radiated noise. Since in the constant radius profile of curve A, the initial valve member impact is at the tip, the profile of curve B raises the portion of the stop 22 facing the free end to delay its contact and lowers the portion of the stop facing the portion of the valve member 21 extending from the root thereby hastening contact of the valve member 21 with stop 22. Initial contact starts at the root and progresses towards the tip of valve member 21 as valve member 21 wraps around stop 22. Since contact of the valve member with the stop defines the fulcrum, opening results in a constantly reducing free length which defines the valve member response which varies with the free length. Referring now to Figure 3, curves C and D correspond to curves A and B, respectively, and represent momentum vs. time from a finite element analysis of valve member impact with the valve stop. Curve C represents the initial impact by the valve member tip which takes place late in the opening stroke, over a short time period, and with high kinetic energy as clearly shown by curve C. In contrast, curve D shows impact starting earlier, and therefore at less kinetic energy, and continuing for a longer period but at a much reduced impact momentum which translates into less noise generation.

Claims: A discharge valve assembly (20) including a valve stop (22) and a valve member (21) having a tip and a root and having a clamped length at said root and a free length extending from said clamped length to said tip, characterized in that said valve stop has along said free length a profile which, as compared to a standard constant radius stop profile, has a first portion which is of an increasing radius relative to a fixed center point (E) and which transitions into a second portion which is of a decreasing radius relative to said center point. The valve assembly according to claim 1, characterized in that said second portion has a radius less than said first portion beyond a point generally corresponding to 90 % of said free length. The valve assembly according to claim 1 or 2, characterized in that engagement between said valve member and said stop takes place over essentially an entire opening movement of said valve member thereby maximizing the duration of, and minimizing the amount of, kinetic energy transfer from said valve member to said stop. The valve assembly according to any one of claims 1 to 3, characterized in that the valve stop (22) has a natural frequency and engagement between the valve member (21) of the valve stop (22) avoids exciting said natural frequency.

Inventors: KUMAR KESHAVA B, MARLER MARK E, PERACCHIO ALDO A, KUMAR, KESHAVA B., MARLER, MARK E., PERACCHIO, ALDO A.
Applicants: CARRIER CORP, CARRIER CORPORATION
Application year: 1994
Main classification: F04C29
IPC codes: F16K15, E03D5, F04C29